Other
Scientific paper
Jun 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985rspsa.399..295h&link_type=abstract
Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Volume 399, Issue 1817, pp. 295-319
Other
7
Scientific paper
The crystal structure of naphthazarin C has been determined by neutron diffraction at 60 and 300 K (λ = 0.895 Å 1 Å = 10-10 m = 10-1 nm) and X-ray diffraction at 300 K. The space group is Pc at 60 K, but P2_1/c at 300 K. There are small but significant differences in cell dimensions at the two temperatures: a = 7.664 (7.915), b = 7.304 (7.262), c = 15.16 (15.284) Å β = 114.60 (114.20)^0; Z = 4; U = 771.6 (801.3) Å^3 (values at 300 K in parentheses). Neutron diffraction shows that the Pc and P2_1/c structures are related by an order-disorder transition at 110±1 K. Structure analysis (1771 reflections; R_F = 0.035; R_W = 0.036) showed that the hydroxyl hydrogens are largely ordered at 60 K, the appropriate molecular formula being 5,8-dihydroxy-1,4-naphthadione. Neutron diffraction measurements at 300 K (1769 reflections; R_F = 0.052) indicated a disordered molecular model with one-half of an hydrogen atom attached to each oxygen. X-ray diffraction measurements on naphthazarin C at 300 K (two independent sets of intensity measurements, one with CuKα and the other with MoKα) support this disordered model. The molecular dimensions for naphthazarin A and B also fit this model. Comparison of the crystal structure of naphthazarin C with those of the A and B polymorphs shows that only the former has intermolecular O-H\cdotsO hydrogen bonding. Thediffraction results combined with the available solid-state n.m.r. data show that there is at room temperature a rapid intramolecular exchange of hydroxylic protons between each pair of oxygen atoms in all three naphthazarin polymorphs. Many 1,3-diketones exist in an enol form in the solid. These enol forms have been reported to be disordered for about twenty molecules at room temperature (this total includes one molecule studied at 108 K, and four amino-imino systems) and ordered systems have been reported for about fifteen molecules. Intermolecular hydrogen bonding occurs only in a few of these crystals.
Curtin D. Y.
Duesler E. N.
Herbstein F. H.
Kapon M.
Kress R. B.
No associations
LandOfFree
Polymorphism of Naphthazarin and its Relation to Solid-State Proton Transfer. Neutron and X-Ray Diffraction Studies on Naphthazarin C does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Polymorphism of Naphthazarin and its Relation to Solid-State Proton Transfer. Neutron and X-Ray Diffraction Studies on Naphthazarin C, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymorphism of Naphthazarin and its Relation to Solid-State Proton Transfer. Neutron and X-Ray Diffraction Studies on Naphthazarin C will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1670187